Somatomedin-C will be extracted from Cohn Fraction IV of outdated human plasma by a new extraction technique and sufficient quantities carried to purity to permit full sequence analysis. Fragments of the intact molecule will be tested for biological activity. The somatomedin binding protein will be characterized and studied for proteolytic activity. The concept will be explored that somatomedin-C binding protein complex represents a prohormone. The site of formation of the complex and hormonal control of the binding protein will be investigated. The role of somatomedin-C in stimulating cell growth will be investigated in cell cultures.